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aga
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Excellent info Magpie.
I shall do the same !
Purifying the CaO made from limestone took a while, although now there is a pot of pure white Ca(OH)2 to stick in the furnace.
I guess buying some tripotassium phosphate, or clean KOH and H3PO4 to make tripot are options, but where's the Fun in that ?
Let's see what the KMnO4 test says when your suggested process is followed.
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careysub
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I have been using potassium carbonate with 75% Everclear (highest proof sold in California), which gets you to 94%, and 3A sieve pellets from there,
though that is expensive (if you do not do vacuum/head desiccation to regenerate).
I'll have to try the Portand cement technique with the 94% ethanol before applying sieves. Thanks!
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deltaH
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I have a bit of a bromance with lime, it's dirt cheap and readily available, but I would like to speculate about another alternative... using a cheap
reactive metal like scrap aluminium.
Saturate your crude alcohol with caustic soda (sodium hydroxide) by stirring it for some time with excess prills and then filter the liquid from the
excess undissolved prills (or simply decant), then add aluminium and fit a good water cooled condenser in the reflux position (but without heating...
the reaction is itself very exothermic once it get's going). When the reaction is done (no more gas evolved), distill to isolate the pure ethanol.
/end speculation
[Edited on 4-2-2016 by deltaH]
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Magpie
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lit. Ca(OH)2 decomposition temp. = 580°C
When I have needed absolute ethanol I found out the hard way (poor yields) that I have to be very careful and conservative in my preparation.
Looking in my lab notebook for that last time I did this (2014) I find:
"Weighed out 107g of slaked lime into large crucible.
3:20PM set muffle furnace for 800°C. Set crucible in furnace.
4:20PM Nearly reached 800°.
6:20PM Turned off muffle furnace.
6:43PM T=600°C, transferred crucible to dessicator to cool."
When distilling the 99.5% ethanol off the CaO I distill it onto mole sieves in an RBF using tapered glass joints to exclude atmospheric moisture.
Also I place a CaCl2 moisture guard tube on the vacuum adapter.
"3A mole sieves are rated at 22wt% H2O absorption. Assuming a very conservative 1% water in the CaO treated ethanol, use the required amount based on
15% absorption." Again I'm being very conservative.
I have used CaC2 and anhydrous CuSO4 for moisture detection per Brewster. (I know, they are not perfect.)
What's this test for water using KMnO4?
The single most important condition for a successful synthesis is good mixing - Nicodem
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blogfast25
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Quote: Originally posted by aga  | The surprising thing is that nobody has jumped in to say 'I always dry my ethanol like this ...' and detailed their usual process.
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Most of us have been drying their EtOH over cement for years, mate. You've just exposed our dirty little secret, that's all... 
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blogfast25
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| Quote: Originally posted by deltaH |
Saturate your crude alcohol with caustic soda (sodium hydroxide) by stirring it for some time with excess prills and then filter the liquid from the
excess undissolved prills (or simply decant), then add aluminium and fit a good water cooled condenser in the reflux position (but without heating...
the reaction is itself very exothermic once it get's going). When the reaction is done (no more gas evolved), distill to isolate the pure ethanol.
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That'll work! Does sound a bit like taking a 155 mm Howitzer to shoot a mouse!
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aga
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Funny how the slightest ego-provocation brought out the 'Here's how I do it' replies.
As an Amateur Chemist i would have offered what i Know Works much earlier, simply to help out another Amateur Chemist.
These responses raise many questions in my mind (such as it is).
Edit:
Too many questions, so i'm out.
[Edited on 4-2-2016 by aga]
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blogfast25
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| Quote: Originally posted by aga | Funny how the slightest ego-provocation brought out the 'Here's how I do it' replies.
As an Amateur Chemist i would have offered what i Know Works much earlier, simply to help out another Amateur Chemist.
These responses raise many questions in my mind (such as it is). |
Huh? Ego-provocations?
So:
| Quote: | | The surprising thing is that nobody has jumped in to say 'I always dry my ethanol like this ...' and detailed their usual process.
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... was a trap?
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aga
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In the trade we call it a Mole Hunt.
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Magpie
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| Quote: Originally posted by aga | Funny how the slightest ego-provocation brought out the 'Here's how I do it' replies.
As an Amateur Chemist i would have offered what i Know Works much earlier, simply to help out another Amateur Chemist.
These responses raise many questions in my mind (such as it is).
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Look at the title of the original post.
The single most important condition for a successful synthesis is good mixing - Nicodem
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blogfast25
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What trade?
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deltaH
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| Quote: Originally posted by blogfast25 | | Quote: Originally posted by deltaH |
Saturate your crude alcohol with caustic soda (sodium hydroxide) by stirring it for some time with excess prills and then filter the liquid from the
excess undissolved prills (or simply decant), then add aluminium and fit a good water cooled condenser in the reflux position (but without heating...
the reaction is itself very exothermic once it get's going). When the reaction is done (no more gas evolved), distill to isolate the pure ethanol.
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That'll work! Does sound a bit like taking a 155 mm Howitzer to shoot a mouse! |
Yeah, but this is where the boy in me fights against the engineer in me
A word of caution to those not aware of this, but it will generate A LOT of hydrogen gas, so not something to do in an enclosed shed unless you want
to blow it to smithereens.
A company very close to me sells aluminium powder by the kilo, dirt cheap, as a metallic filler for plastic composites (eqv. 3.65 euros/kg incl.).
Caustic soda is sold in 25kg amounts for (eqv. ~1.35 euro/kg, ok, actually a little cheaper, but I like easy math).
1kg aluminium powder will dispose of exactly 2kg water based on stoichiometry, but you need 1.5kg caustic soda if you going the alkaline activation
route.
On that theoretical basis, 1kg aluminium powder can treat 50kg 96 wt.% ethanol, at a cost of 1 euro/10kg (~12.5l) wet ethanol... not so bad.
For completeness, the reaction in question is of course:
Al(s) + 3H2O(l) + NaOH(aq) => NaAl(OH)4(s) + 1.5H2(g) + heat
One could also use a little mercury or salt thereof to activate the aluminium and so dispense with having to use caustic soda, but I'm not a fan of
working with [and having to recovery] mercury. Incidentally, using mercury, one can prepare aluminium alkoxides with alcohols directly from the metal.
So one should not use too much of an excess of aluminium or you will consume alcohol after first consuming all the water.
[Edited on 5-2-2016 by deltaH]
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